Acousto-optic laser microscopy system

ABSTRACT

A laser scanning microscopy system includes a laser whose beam is modified by an acousto-optic deflector that includes an optical element having a surface with one or more steps formed thereon; a conductive layer formed on the surface with the steps; one or more crystals secured to each step; and electrodes positioned on each surface of each crystal.

This application claims priority to, commonly filed applications on Apr.7, 2023 with U.S. Pat. Nos. 18,132,025, 18,132,034, 18,132,047,18,132,054, 18,132,058, 18,132,064, 18,132,069, 18,132,070, 18,132,074the contents of which are incorporated by reference.

BACKGROUND

The present invention relates to an acousto-optic transducer for a lasersystem.

Laser scanning microscopy is an important technique in modern microscopyfor high-resolution imaging of biological and non-biological samples. Itallows for non-invasive, non-destructive, and high-speed imaging ofsamples with high spatial and temporal resolution. It is particularlyuseful for studying biological structures and processes at the cellularand subcellular levels. The need for laser scanning microscopy arisesfrom the limitations of traditional light microscopy, which is oftenlimited by diffraction of light and cannot resolve structures smallerthan the wavelength of light. Laser scanning microscopy overcomes thislimitation by using lasers to excite fluorescent molecules or otherprobes, allowing for sub-diffraction-limited imaging of structures andprocesses in living cells and tissues.

SUMMARY

In one aspect, a laser scanning microscopy system includes a laser whosebeam is modified by an acousto-optic deflector that includes an opticalelement having a surface with one or more steps formed thereon; aconductive layer formed on the surface with the steps; one or morecrystals secured to each step; and electrodes positioned on each surfaceof each crystal.

In another aspect, s laser scanning microscopy system includes:

-   -   a laser for providing a light source;    -   a scanning system for scanning the laser beam across a sample;    -   a detector for detecting emitted light from the sample; and    -   a phased array acousto-optic deflector (AOD) for controlling the        direction and intensity of the laser beam.

Implementations of the aspect can include one or more of the following.The AOD comprises multiple AODs operating at different frequencies toachieve high-speed and accurate beam steering.

3. The AOD delivers light to specific regions of a sample for performingoptogenetics. The AOD controls the laser beam intensity and timing andperforms fluorescence lifetime imaging microscopy (FLIM). The AOD isused for performing stimulated emission depletion (STED) microscopy bymodulating the laser beam intensity to create super-resolution images.The AOD is used for performing two-photon excitation microscopy (2PEM)by controlling the laser beam intensity and frequency to excitefluorophores deep within a sample. An adaptive optics system can be usedfor correcting for aberrations in the laser beam path or a confocalsystem for reducing out-of-focus light and improving image contrast. TheAOD has the optical element with a slanted end, wherein the slanted endcomprises a compound angle to move reflected sound field out of a laserbeam working range, wherein the slanted end forms a 30 degree anglemeasured from a long side of the optical element to a short side of theoptical element, and wherein a surface of the slanted end comprises a 2degree slope, and wherein the optical element comprises germanium,tellurium dioxide (TeO2), lithium niobate, PZT, fused silica,chalcogenide glasses, glass.

In a further aspect, a method to perform microscopy includes:

-   -   providing a light source with a laser;    -   controlling the direction and intensity of the laser beam using        a phased array AOD with one or more steps;    -   scanning the laser beam across a sample;    -   detecting emitted light from the sample to generate an image of        the sample.    -   applying the laser beam to an optical element having one or more        steps each with a predetermined height and one or more crystals        or transducers on the one or more steps;    -   impedance matching the electrical input of the transducers to a        predetermined impedance load;    -   providing an electrical input to deflect the laser at the two or        more frequencies.

In one implementation, an acousto-optic deflector includes an opticalelement having a surface with one or more steps formed thereon; aconductive layer formed on the surface with the steps; one or morecrystals secured to each step; and one or more electrodes positioned onthe surface of the one or more crystals.

Implementations of the above aspect can include one or more of thefollowing. A tuning element can be used to match a predeterminedimpedance. The tuning element can provide an output impedance of 50 ohmsfor one use case. The tuning element can have inductive and capacitivepassive components. In one embodiment, the tuning element can be a 1:1balun, 4:1 transformer, a capacitor, and an inductor. The opticalelement comprises a slanted end. The tuning element matches a deflectoroutput impedance at 40 MHz and at 60 MHz to a 50 ohm impedance. Theslanted end can have a compound angle designed to drive the reflectedsound field out of a laser beam working range so that no reflected soundwave can impact laser performance. In one specific design, the slantedend forms a 30 degree angle measured from a long side of the opticalelement to a short side of the optical element and the surface of theslanted end has a 2 degree slope. The optical element can be germanium,tellurium dioxide (TeO2), lithium niobate, PZT, fused silica,chalcogenide glasses, or glass, for example.

In another aspect, a method to form a phased-array transducer includes

-   -   grinding an optical element to form two or more steps each with        a predetermined height;    -   depositing a conductive layer (gold) over the one or more steps;    -   attaching one or more crystals or transducers on the one or more        steps; and    -   attaching electrodes to the top and bottom of each transducer.

Implementations of the above aspect can include one or more of thefollowing. The method includes matching the input of the transducers toa predetermined impedance. A tuning element can be connected to thetransducers with an output impedance of 50 ohms. The tuning elementincludes inductive and capacitive passive components. The tuning elementcan have a 1:1 balun, a 4:1 transformer, a capacitor, and an inductor.The optical element can have a slanted end, wherein the slanted endcomprises a compound angle to move reflected sound field out of a laserbeam working range. Te slanted end forms a 30 degree angle measured froma long side of the optical element to a short side of the opticalelement. A surface of the slanted end has a 2 degree slope. The opticalelement comprises germanium, tellurium dioxide (TeO2), lithium niobate,PZT, fused silica, chalcogenide glasses, glass. The tuning elementmatches a deflector output impedance at 40 MHz and at 60 MHz to a 50 ohmimpedance.

In another aspect, a method to deflect a laser beam includes:

-   -   applying the laser beam to an optical element having one or more        steps each with a predetermined height and one or more crystals        or transducers on the one or more steps;    -   impedance matching the electrical input of the transducers to a        50-ohm load;    -   providing an electrical input to deflect the laser at the two or        more frequencies; and    -   generating a sound field in the optical element to deflect a        laser beam based on two or more frequencies.

In a further aspect, a method to form an opto-acoustic deflectorincludes

-   -   grinding an optical element to provide one or more steps each        with a predetermined height;    -   depositing a layer of gold over the one or more steps; and    -   attaching one or more crystals or transducers on the one or more        steps.

Implementations of the above aspect can include one or more of thefollowing. The method includes tuning the electrical output for 40 MHzand 60 MHz output. A slanted end is formed on the optical element with acompound angle to move reflected sound field out of a laser beam workingrange. The slanted end forms a 30 degree angle measured from a long sideof the optical element to a short side of the optical element. A surfaceof the slanted end comprises a 2 degree slope.

In another aspect, a method to form and to operate an opto-acousticdeflector includes:

-   -   grinding an optical element to form one or more steps each with        a predetermined height;    -   depositing a conductive layer (gold) over the one or more steps;    -   attaching one or more crystals or transducers on the one or more        steps;    -   attaching electrodes to the top and bottom of each transducer;    -   impedance matching the electrical input of the transducers to a        50-ohm load;    -   receiving an electrical input to deflect the laser at the two or        more frequencies; and    -   generating a sound field in the optical element to deflect a        laser beam based on two or more frequencies.

Implementations can include one or more of the following. The method caninclude tuning the electrical output for 40 MHz and 60 MHz output. Themethod includes forming a slanted end on the optical element. The methodfurther includes forming a compound angle to move reflected sound fieldout of a laser beam working range. The slanted end forms a 30 degreeangle measured from a long side of the optical element to a short sideof the optical element. A surface of the slanted end comprises a 2degree slope. The method includes grinding the optical element, whichcan be germanium, tellurium dioxide (TeO2), lithium niobate, PZT, fusedsilica, chalcogenide glasses, glass, among others.

Advantages of the system may include one or more of the following. Thedeflector can operate with two distinct frequencies, for example at 40and 60 MHz, resulting in a single device that can do the job of two. Thedeflector thus is smaller, lower power, and higher matching behaviorover versions that require two separate deflectors each geared toward aparticular frequency. The acousto-optic deflector is a versatile devicethat provides precise and efficient control over the direction of alaser beam. Its ability to scan and steer laser beams in a specificdirection makes it an essential tool in various applications such asmicroscopy, laser printing, and laser communication.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A-1B show an exemplary phased array opto-acoustic deflector.

FIG. 2A-2B show exemplary processes for forming and using the deflectorof FIG. 1A.

FIG. 3 shows an exemplary tuning element that is coupled to theelectrodes to match a predetermined impedance.

FIG. 4-5 show exemplary opto-acoustic laser systems.

DESCRIPTION

FIG. 1A shows an exemplary phased array opto-acoustic system. In aphased array opto-acoustic system, a pulsed laser beam is used togenerate acoustic waves in a sample chamber such as optical element thatreceives the laser beam. The laser beam path is altered by the soundgenerated by the opto-acoustic elements in a transducer coupled to theoptical element.

FIG. 1A-16 show a device 10 having stepped surfaces 12 and 16 on oneend, and an angled end 30 opposite to the stepped surfaces 12 and 16.Turning now to FIG. 1A, an exemplary phase-array device includes anoptical element having a surface with one or more steps formed thereon,where the optical element has at least two step heights. The differentheights of the steps affect the acousto-optic RF frequency responses.

Transducers are mounted above the stepped surfaces 12 and 16, with oneside of each transducer coupled to RF inputs 20-21 respectively, and theother side of the transducer connected to ground 18. The phased arraytransducer array has a plurality of transducers mounted on a topsurface, with each transducer at a different height. Each transducer inthe array is positioned at different vertical positions, such as atdifferent heights above a sample chamber surface. One example of such anarray is a linear transducer array, in which a linear array oftransducers is arranged along a surface, with each transducer positionedat a different height. Another example is a 2D transducer array, inwhich a grid of transducers is positioned at different heights to form a2D array.

As shown in FIG. 1B, the optical element 10 has a surface with one ormore steps 12 formed thereon, where the height of each step on thesurface of the optical element can be precisely controlled during themanufacturing process, which allows for the creation of specificacousto-optic frequency responses. The step height can be chosen tomatch the wavelength of RF input, creating a specific phase shift, or toprovide a specific diffraction angle. The height of each step can alsoaffect the coupling between the acoustic wave and the optical wave,which determines the efficiency and bandwidth of the acousto-opticinteraction. Grinding or subtractive techniques can be applied to thesurface of the optical element to form one or more steps spaced apart onthe surface, where the height of each step affects the acousto-optic RFfrequency response. This provides a versatile and precise tool formanipulating the interaction between acoustic waves and optical waves.This technology is useful in a variety of applications, such as laserbeam modulation, scanning, and frequency shifting.

In some cases, the steps 12 on the surface of the optical element canhave a plurality of different heights. This can be done to create a morecomplex RF frequency response, which can be useful for certainapplications. Transducer 13 is adhesively bonded with a thin epoxy layer15 to the top to steps 12. This is done when the device 10 is insertedinto its spot in the receptacle of FIG. 4C, applying a thin layer ofepoxy 15 on top of step 13, and then by operation of vacuuming thetransducer 13 to secure it to the bottom of the piston and by airpressure lowering the piston with the top of step 12 and evenly applythe epoxy to secure the transducer 13 to device 10.

By having steps with different heights, the acousto-optic device can bedesigned to deflect light at multiple angles or frequencies. This can beused, for example, in laser scanning systems, where the deflection angleof the incident laser beam needs to be precisely controlled.

The optical and acoustic elements in a phased array opto-acoustic deviceare arranged in a specific pattern to allow for precise control of theacoustic waves generated and detected. The optical elements transmit thelaser beam through the sample chamber. The acoustic elements may includea phased array of transducers, which are used to control the directionand intensity of the acoustic waves.

In these applications, the optical element is made of a material thatcan support a propagating acoustic wave, such as a crystal or glass. Theacoustic wave is created by a transducer, and its frequency is modulatedby an applied RF signal. The optical element is made of a material thatcan support a propagating acoustic wave, such as a crystal or glass. Theacoustic wave is created by a transducer, and its frequency is modulatedby an applied RF signal. the height of each step affects theacousto-optic RF frequency response, is typically used in acousto-opticmodulators and deflectors. One embodiment of the instant device enablesa single device to work at two distinct frequencies, enabling one deviceto be used instead of two separate devices.

The optical element has a surface with one or more steps formed thereon,where the height of each step on the surface of the optical element canbe precisely controlled during the manufacturing process, which allowsfor the creation of specific acousto-optic frequency responses. The stepheight can be chosen to match the wavelength of the incident light,creating a specific phase shift, or to provide a specific diffractionangle. The height of each step can also affect the coupling between theacoustic wave and the optical wave, which determines the efficiency andbandwidth of the acousto-optic interaction.

Grinding or subtractive techniques can be applied to the surface of theoptical element to form one or more steps spaced apart on the surface,where the height of each step affects the acousto-optic RF frequencyresponse. This provides a versatile and precise tool for manipulatingthe interaction between acoustic waves and optical waves. Thistechnology is useful in a variety of applications, such as laser beammodulation, scanning, and frequency shifting.

In some cases, the steps on the surface of the optical element can havea plurality of different heights. This can be done to create a morecomplex RF frequency response, which can be useful for certainapplications.

By having steps with different heights, the acousto-optic device can bedesigned to deflect light at multiple angles or frequencies. This can beused, for example, in laser scanning systems, where the deflection angleof the incident laser beam needs to be precisely controlled.

FIG. 2A shows an exemplary process to form a phased-array transducer.The process includes the following operations:

-   -   grinding an optical element to form two or more steps each with        a predetermined height;    -   depositing a conductive layer over the one or more steps;    -   attaching one or more crystals or transducers on the one or more        steps; and    -   attaching electrodes to the top and bottom of each transducer.

In more details, the process of creating steps with different heights onthe surface of an optical element can be done using various techniques,including etching or grinding. Etching can be used to selectively removematerial from the surface, while grinding can be used to selectivelyremove material from certain areas of the surface. The end result is asurface with steps of varying heights that can be used to control the RFfrequency response of the acousto-optic device.

The tools used to grind the optical element with the steps may varydepending on the material of the optical element and the desiredprecision of the steps. Some common tools used for grinding opticalelements include diamond-tipped tools, abrasive wheels, andlapping/polishing pads.

Diamond-tipped tools are often used for grinding hard and brittlematerials such as glass and some ceramics. These tools are made of athin metal shank with a small diamond grit on the tip. The diamond gritis used to scratch away material from the optical element, creating thedesired steps. Diamond-tipped tools can achieve high precision andsmooth surface finishes.

Abrasive wheels are another common tool used for grinding opticalelements. These wheels are made of abrasive particles bonded to a wheelshape. The abrasive particles can be made of materials such as siliconcarbide or aluminum oxide, and the bond can be made of materials such asresin or vitrified ceramic. Abrasive wheels are often used for grindingsofter materials such as plastic or some metals. These wheels can removematerial quickly but may not achieve the same precision asdiamond-tipped tools.

Lapping and polishing pads are used for finishing the optical elementafter grinding. These pads are made of a soft material such as felt orpolyurethane foam and are coated with a fine abrasive material such asdiamond paste. The optical element is placed on the pad and moved in acircular motion to achieve a smooth surface finish.

Other tools that may be used for grinding optical elements includegrinding machines, CNC equipment, and ultrasonic machining tools. Thechoice of tool depends on the material of the optical element, thedesired precision, and the production volume.

Cleaning of the optical element surface is an essential step to ensurethe adhesion of the subsequent gold layer. The cleaning operationtypically involves the following steps:

-   -   Rinse the optical element with deionized water or a cleaning        solvent to remove any loose particles or debris on the surface.    -   Immerse the optical element in a mild acid solution, such as        hydrochloric acid or sulfuric acid, to remove any organic or        inorganic contaminants. The duration of the immersion depends on        the type and level of contamination and typically ranges from a        few seconds to several minutes.    -   Rinse the optical element with deionized water to remove any        residual acid and neutralize the surface.    -   Dry the optical element using a stream of dry nitrogen or argon        gas or a cleanroom-compatible drying method such as spin-drying        or vacuum-drying.    -   Inspect the optical element surface under a microscope or with a        cleanroom-compatible surface analysis tool to ensure that the        surface is free of particles, scratches, or defects that can        affect the performance of the subsequent gold layer deposition.

By following these steps, the optical element surface can be preparedfor the deposition of a uniform and adherent gold layer.

The height of each step on the surface of the optical element can beprecisely controlled during the manufacturing process, which allows forthe creation of specific acousto-optic frequency responses. The stepheight can be chosen to match the wavelength of the incident sound,creating a specific phase shift, or to provide a specific diffractionangle. The height of each step can also affect the coupling between theacoustic wave and the optical wave, which determines the efficiency andbandwidth of the acousto-optic interaction.

In an acousto-optic modulator, the applied RF signal modulates thefrequency of the acoustic wave, which in turn modulates the phase oramplitude of the optical wave passing through the optical element. Themodulation depth and frequency bandwidth of the modulator depend on theheight and spacing of the steps on the optical element. The applied RFsignal generates an acoustic wave that travels along the surface of theoptical element, causing the incident optical beam to diffract at aspecific angle. The applied RF signal modulates the frequency of theacoustic wave, which in turn modulates the phase or amplitude of theoptical wave passing through the optical element.

A conductive layer is formed on the surface with the steps. In somecases, a conductive layer such as gold is deposited on the surface withthe steps. This is done to allow for an electrical contact to be madewith the surface, which is necessary for applying the RF signal to theacousto-optic device. The conductive layer also helps to reduce anyunwanted reflections that may occur at the surface, which can affect theperformance of the device.

First, a layer of nichrome is formed on the surface of the opticalelement since gold does not bond well with the optical element. Then alayer of gold is deposited above the nichrome layer. The conductivelayer is typically deposited using a process called physical vapordeposition (PVD) or sputtering. In PVD, a thin film of gold is depositedon the surface by evaporating the metal in a vacuum chamber and allowingit to condense onto the surface. In sputtering, a plasma is used toeject gold atoms from a target material and deposit them onto thesurface.

The equipment used to deposit a fine layer of gold over the steps on theoptical element is called a physical vapor deposition (PVD) system. PVDis a process where a solid material is vaporized in a vacuumenvironment, and the resulting vapor condenses onto a substrate to forma thin film.

In this case, the gold is evaporated in a vacuum chamber using anelectron beam gun or a resistive filament. The vaporized gold atomstravel in a straight line towards the substrate, where they condense andform a thin layer on the surface of the optical element. The thicknessof the gold layer can be controlled by adjusting the deposition rate andthe deposition time.

The PVD system typically includes a vacuum chamber, a substrate holder,a source of gold, and a means to evaporate the gold. The substrateholder is designed to hold the optical element with the steps facingupwards and is positioned in the vacuum chamber. The chamber is thenevacuated to a high vacuum level, typically in the range of10{circumflex over ( )}-6 to 10{circumflex over ( )}-7 torr, to preventcontamination of the gold layer.

The gold source is typically a solid piece of gold that is heated by anelectron beam or a resistive filament. As the gold is heated, itevaporates and condenses on the surface of the optical element. Thedeposition rate and deposition time can be controlled by adjusting thepower of the heating source and the distance between the source and thesubstrate.

Once the gold layer is deposited, the optical element is removed fromthe vacuum chamber and inspected for uniformity and thickness. Thethickness of the gold layer is typically in the range of a few hundrednanometers to a few microns, depending on the application.

Overall, the PVD system is a precise and reliable method for depositinga thin layer of gold on the surface of the optical element with thesteps, ensuring optimal performance of the acousto-optic deflector.

A transducer or a crystal is then affixed to each step, preferably atdifferent heights based on the height of the steps. The crystal issecured to each step of an optical element using epoxy bonding in oneembodiment. The crystal is placed in contact with the conductive layeron the surface of the optical element. Electrodes positioned on eachsurface of each crystal, one connected to ground and one connected to anRF signal driving the crystal.

After the conductive layer is deposited and the crystal affixed to theoptical element, electrical contacts are typically made to the surfaceusing wire bonding or other techniques. Electrodes are then connected toeach side of the crystal. Energy applied to the crystal generates anacoustic wave in response to an applied RF signal, and the electrodesare used to apply the RF signal to the crystal. An RF signal is thenapplied to the contacts, which generates the acoustic wave thatmodulates the refractive index of the acousto-optic material anddeflects the incident light.

The electrodes are made of a conductive material, such as gold oraluminum, and are placed on opposite sides of the crystal. When an RFsignal is applied to the electrodes, it generates an acoustic wave inthe crystal, which can then be used to modulate the laser beam appliedto the optical element.

An RF signal applied to the crystal would generate an acoustic wave,which would propagate through the crystal and into the optical element.The acoustic wave would then modulate the refractive index of theoptical element, causing it to diffract or deflect an incident beam oflight.

The positioning and design of the electrodes can be critical to theperformance of the acousto-optic device. The spacing between theelectrodes, the shape of the electrodes, and the applied voltage allaffect the frequency response of the device.

FIG. 2B shows an exemplary method to deflect a laser beam that includes:

-   -   applying the laser beam to an optical element having one or more        steps each with a predetermined height and one or more crystals        or transducers on the one or more steps;    -   impedance matching the electrical input of the transducers to a        50-ohm load;    -   providing an electrical input to deflect the laser at the two or        more frequencies; and    -   generating a sound field in the optical element to deflect a        laser beam based on two or more frequencies.

Other methods to form an opto-acoustic deflector include:

-   -   grinding an optical element to provide one or more steps each        with a predetermined height;    -   depositing a layer of gold over the one or more steps; and    -   attaching one or more crystals or transducers on the one or more        steps.

FIG. 3 shows an exemplary tuning element that is coupled to theelectrodes to match a predetermined impedance. The tuning element isused to match the predetermined impedance of the acousto-optic phasedarray transducers. The tuning element is typically an inductor with apredetermined coil length and a variable capacitor or a trimmercapacitor that is adjusted to match the impedance of the system. This isimportant to ensure maximum power transfer between the amplifier and theacousto-optic deflector, which leads to better performance andefficiency. The tuning element can be adjusted by a technician or can beautomated using a feedback control loop to continuously monitor andadjust the impedance.

The tuning element is typically used to match the impedance of theacousto-optic deflector to the impedance of the driving circuit, whichis often 50 ohms. This ensures maximum power transfer between theamplifier and the acousto-optic deflector. The impedance matching canhelp to minimize the reflection of the signal, which can cause unwantedinterference and signal degradation.

The tuning element can be used to match the impedance of theacousto-optic deflector at specific RF frequencies to a 50-ohmimpedance. This is typically done using a matching network or filter,which can be adjusted to achieve the desired impedance match. Forexample, if the deflector has an output impedance of 40 MHz and 60 MHz,a tuning element can be designed to match those frequencies to 50 ohms.

The tuning element can be implemented using various techniques, such asa lumped element filter, a distributed element filter, or a combinationof both. The choice of technique depends on various factors such as thefrequency range, the required bandwidth, and the physical size of thetuning element.

Once the tuning element is designed, it can be coupled to the electrodesof the acousto-optic deflector to achieve the desired impedance match.This can be done using various coupling techniques such as wire bondingor soldering. The impedance match ensures that maximum power istransferred from the RF amplifier to the acousto-optic deflector, whichimproves its efficiency and performance.

Opposite to the surface with the steps on the optical element is aslanted end with a compound angle to direct any reflected sound fieldaway from the laser beam working range. This can help to reduce unwantedinterference and improve the overall performance of the acousto-opticdeflector. The compound angle can be designed to achieve the desireddeflection angle for the laser beam while also minimizing any unwantedreflections or diffraction effects. The exact design of the slanted endwill depend on the specific application and requirements of theacousto-optic deflector.

To prevent these issues, it is important to carefully control thedeposition process and ensure that the gold layer is well adhered to theoptical element's surface. Additionally, the amount of epoxy used shouldbe carefully controlled and optimized to ensure strong bonding betweenthe crystals and the surface without creating unnecessary attenuation ofthe acoustic waves. Quality control and testing should also be performedto ensure that the opto-acoustic deflector meets the requiredspecifications for performance and reliability.

To form a slanted end of the optical element with a 30 degree anglemeasured from a long side to a short side and a surface with a 2 degreeslope, the following steps can be taken:

-   -   Obtain an optical element made of the desired material, such as        germanium or tellurium dioxide (TeO2).    -   Determine the dimensions of the optical element and mark the        area where the slanted end will be located.    -   Use a precision saw or cutting tool to cut the slanted end at        the desired angle. This can be done by tilting the cutting tool        at a 30 degree angle relative to the long side of the optical        element.    -   Use a precision grinding tool, such as a diamond or abrasive        wheel, to grind the surface of the slanted end to achieve the        desired 2 degree slope. This can be done by adjusting the angle        and pressure of the grinding tool.    -   Inspect the surface of the slanted end to ensure that it is        smooth and free of any cracks or defects.    -   Clean the surface of the slanted end using a gentle solvent,        such as isopropyl alcohol, to remove any debris or particles.    -   Optionally, apply a protective coating, such as a thin layer of        anti-reflection coating or a metal film, to the surface of the        slanted end to improve its optical properties and prevent damage        from handling or exposure to the environment.

Overall, the key to forming a slanted end with the desired angle andslope is to use precision tools and techniques to achieve the desiredshape and surface quality, while minimizing any damage or stress to theoptical element.

The optical element can be germanium, tellurium dioxide (TeO2), lithiumniobate, PZT, fused silica, chalcogenide glasses, glass. The choice ofmaterial for the optical element depends on various factors such as thedesired optical properties, thermal and mechanical stability, and thespecific application for which the element will be used.

The choice of crystal for an opto-acoustic laser system depends on thespecific application and the properties of the crystal. Some of thefactors that are typically considered when selecting a crystal foropto-acoustic applications include the crystal's acoustic and opticalproperties, as well as its thermal and mechanical stability, amongothers. One commonly used crystal for opto-acoustic applications islithium niobate (LiNbO3). LiNbO3 has excellent acoustic properties, witha high acoustic velocity and a low acoustic attenuation, which makes itideal for generating and detecting acoustic waves. It also has strongnonlinear optical properties, which can be used for frequency conversionand modulation of the laser beam.

Another crystal that is commonly used for opto-acoustic applications isquartz (SiO₂). Quartz has a high acoustic velocity and a low acousticattenuation, making it ideal for acoustic wave generation and detection.It is also highly transparent in the infrared region, which is usefulfor many laser applications.

Other crystals that are sometimes used for opto-acoustic applicationsinclude gallium arsenide (GaAs), gallium nitride (GaN), and sapphire(Al₂O₃). These crystals have specific properties that make them suitablefor certain applications, such as high-temperature stability or highoptical nonlinearity.

The choice of crystal for an opto-acoustic laser system depends on thespecific requirements of the application, such as the desired acousticand optical properties, as well as the thermal and mechanical stabilityof the crystal.

Some commonly used materials for acousto-optic devices include:

-   -   Germanium: Germanium is a common material for acousto-optic        modulators operating in the mid-infrared region due to its high        refractive index and low absorption coefficient in this range.    -   Tellurium dioxide (TeO2): TeO2 is a widely used material for        acousto-optic devices due to its high electro-optic coefficient        and wide transparency range from UV to mid-infrared.    -   Lithium niobate (LiNbO3): LiNbO3 is a well-known electro-optic        material with high electro-optic coefficients, making it a        popular choice for high-speed acousto-optic modulators and        deflectors.    -   PZT: PZT or lead zirconate titanate is a piezoelectric material        with high coupling coefficients, making it an ideal choice for        transducers in acousto-optic devices.    -   Fused silica: Fused silica has a high laser damage threshold and        low coefficient of thermal expansion, making it suitable for        high-power applications.    -   Chalcogenide glasses: These are glasses containing elements from        the chalcogen group such as sulfur, selenium, and tellurium.        They have high refractive indices, wide transparency ranges, and        are suitable for acousto-optic devices in the mid-infrared        range.    -   Glass: Different types of glasses can be used for acousto-optic        devices depending on the specific application and desired        properties. For example, borosilicate glass is commonly used for        high-power applications, while crown glass is used for its high        refractive index.

Next, a description of the process to form an opto-acoustic deflector isdetailed. The operation includes the following:

Grinding the Optical Element: The first step is to grind the opticalelement to provide one or more steps, each with a predetermined height.This step involves precise grinding to create the desired step heightsfor optimal acousto-optic performance.

Deposition of Conductive Layer: After grinding, a layer of gold isdeposited over the one or more steps of the optical element. To improvebonding of the gold to the optical layer, a layer of nichrome is firstdeposited on the optical element, and the gold conductive layer issubsequently formed. The gold layer provides a conductive surface thatcan be used for attachment of the crystals or transducers.

Attachment of Crystals or Transducers: One or more crystals ortransducers are attached on the one or more steps of the opticalelement. These crystals or transducers generate acoustic waves thatinteract with light passing through the optical element and deflect itin a controlled manner. The attachment process can involve a variety oftechniques, such as epoxy bonding, soldering, or mechanical clamping.

Capturing Electrical Output: Electrical signals are generated by thecrystals or transducers when they are subjected to acoustic waves. Theseelectrical signals are captured using specialized electronics designedto amplify and process them for further analysis.

Impedance Matching: The final step is to impedance match the electricaloutput to a 50-ohm load. This involves the use of a tuning element suchas a matching network or a transformer, which helps to adjust theimpedance of the electrical signal to match the required load. This stepis critical to ensure maximum power transfer and minimum signal loss.

Once the impedance matching is complete, the opto-acoustic deflector isready for use. It can be integrated into various optical systems todeflect and control light with high precision, making it useful for avariety of applications such as laser printing, holography, and opticalcommunication.

In the context of a transducer array with each transducer at a differentheight, it is possible to achieve the height difference by grinding thesurface on which the transducers are mounted to create a steppedprofile. This can be accomplished using precision grinding tools andtechniques, such as diamond grinding or abrasive blasting.

The grinding process involves removing material from the surface in acontrolled manner to create a series of steps or terraces with differentheights. The transducers can then be mounted on the surface at thedesired heights, with each transducer positioned on a different terrace.The height difference between the transducers can be controlled byadjusting the height and spacing of the terraces during the grindingprocess.

Grinding can be a precise and effective method for creating a steppedsurface with controlled heights for a transducer array. The result ofthe grinding process forms a set of pedestals to mount transducers tothe pedestal array, with at least two transducers with differentheights.

Attaching a transducer to a surface of the stpes can be done using anepoxy spread in an even and thin manner. This method involves applying alayer of epoxy or other adhesive material to the surface and thenplacing the transducer on top of the adhesive. The epoxy is then allowedto cure, creating a strong and permanent bond between the transducer andthe surface.

As each transducer may be positioned at a different height, an array ofspreaders can be used to apply the epoxy to the surface in a controlledand uniform manner. Each application head can be customized according tothe desired height, allowing the epoxy to be applied to specific areasof the surface to create the desired stepped profile. The use of anarray of spreaders, each with self adjustable heights, can provide ahigh degree of control and precision in the placement of thetransducers, allowing for a more uniform and consistent array. However,specialized equipment is needed to create and operate the array ofindividually pliant spreaders so that each spreader automaticallyconforms to the different step heights.

The array of individually pliant spreaders can be pneumatically actuatedto allow for precise control over the height of each transducer in thearray. Pneumatic actuation involves using compressed air to control themovement of the spreaders and to stop them at the desired height foreach surface portion.

By using pneumatic actuation with the pliant or conformal heads, thespreaders can be controlled to stop at the exact height required foreach transducer, allowing for an even spread of the epoxy and a precisepositioning of the bonding pressure on the transducers to ensure optimumbond between the transducer and the corresponding step on the opticalelement. This method can be particularly useful for creating an arraywith a plurality of transducers, as it allows for the process to beautomated and ensures a consistent and accurate result.

The use of pneumatically actuated spreaders also offers other advantagesover manual methods, such as greater speed, efficiency, andrepeatability. It can also reduce the risk of human error andvariability in the epoxy spreading process, which can lead to moreconsistent and reliable results.

Using pneumatically actuated spreaders to create a transducer array witheach transducer at a different height can be a viable option forapplications that require precise and uniform positioning of thetransducers. The suitability of this method will depend on the specificrequirements of the application and the available resources andexpertise.

Attaching the crystals or transducers to the layer of gold on theoptical element can be done through several methods, includingultrasonic bonding, thermal compression bonding, or epoxy bonding.

Ultrasonic bonding involves placing the crystal or transducer onto thelayer of gold and using ultrasonic waves to generate heat and create abond between the two materials. This method is commonly used for smallercrystals and transducers.

Thermal compression bonding involves applying heat and pressure to thecrystal or transducer, causing it to bond with the layer of gold. Thismethod is commonly used for larger crystals and transducers.

Epoxy bonding involves applying a small amount of epoxy adhesive to thecrystal or transducer and placing it onto the layer of gold. Theadhesive is then cured, creating a strong bond between the crystal ortransducer and the gold layer.

Regardless of the method used, care should be taken to ensure that thecrystal or transducer is properly aligned with the gold layer to ensureoptimal performance of the opto-acoustic deflector.

The thickness of the epoxy layer used to attach the crystals to thelayer of gold in an opto-acoustic deflector must be as thin as possiblefor several reasons:

-   -   Minimizing acoustic attenuation: The epoxy layer can attenuate        the acoustic wave generated by the transducer, which can reduce        the deflection efficiency of the device. A thinner epoxy layer        can minimize the attenuation of the acoustic wave and improve        the device's performance.    -   Avoiding acoustic interference: The epoxy layer can also cause        acoustic interference, particularly if it is too thick. This        interference can result in unwanted diffraction or scattering of        the acoustic wave, which can also reduce the device's        performance. A thinner epoxy layer can help to avoid this        problem.    -   Minimizing optical distortion: The epoxy layer can also        introduce optical distortion due to its refractive index. This        distortion can be particularly problematic if the optical        element is used in a laser beam steering application where        precise control of the beam direction is critical. A thinner        epoxy layer can help to minimize this distortion and improve the        device's performance.

Overall, a thinner epoxy layer can help to improve the efficiency,accuracy, and reliability of an opto-acoustic deflector.

The process of applying an ultra-thin layer of epoxy involves severalsteps, including:

-   -   Preparation: The surface of the gold layer on the optical        element must be thoroughly cleaned to remove any contaminants        that may interfere with the adhesion of the epoxy. This can be        done using a combination of solvents and ultrasonic cleaning.    -   Mixing: The epoxy is typically a two-part adhesive that must be        mixed together in precise proportions. This is often done using        a syringe or other dispensing device to ensure accuracy.    -   Dispensing: Once mixed, the epoxy is dispensed onto the surface        of the gold layer. To achieve an ultra-thin layer, a dispensing        device with a small aperture is typically used.    -   Spreading: The epoxy is spread evenly across the surface of the        gold layer using a micro-manipulator or other precision tool.        This must be done carefully to avoid creating air bubbles or        other imperfections.    -   Curing: Once the epoxy has been applied, it must be cured        according to the manufacturer's instructions. This typically        involves heating the optical element to a specific temperature        for a set amount of time.

By using precise dispensing and spreading techniques, it is possible toapply an ultra-thin layer of epoxy that is only a few microns thick.This is important for acousto-optic devices because it minimizes anyinterference that the epoxy layer may have on the performance of thedevice.

Delamination of the gold layer and epoxy failure can both be potentialissues in the manufacturing process of an opto-acoustic deflector. Golddelamination can occur due to poor adhesion between the gold layer andthe optical element's surface. This can be caused by inadequate cleaningof the surface before deposition, or by the use of inappropriateconditions during the deposition process. If the gold layer delaminates,it can cause the crystals to detach from the surface, resulting in thefailure of the entire device. Epoxy failure can occur due to a number offactors. One issue can be improper mixing of the epoxy, leading toinconsistencies in the hardness and adhesive properties of the epoxy.Another issue can be the use of too much or too little epoxy, which canaffect the bonding strength and stability of the crystals. In addition,if the epoxy layer is too thick, it can lead to acoustic waveattenuation, reducing the efficiency of the opto-acoustic deflector.

If the epoxy layer is too thick, it can create several issues in theopto-acoustic deflector. Firstly, a thick layer of epoxy can cause anuneven surface, which can affect the optical properties of thedeflector. This can result in distortion, scattering, or attenuation ofthe laser beam passing through the deflector. Secondly, a thick layer ofepoxy can increase the distance between the crystal and the gold layer,which can affect the efficiency of the acousto-optic interaction. Thiscan result in lower deflection efficiency, higher power consumption, orincreased heat generation.

Additionally, a thick layer of epoxy can cause mechanical stress on thecrystal and the gold layer. As the epoxy cures, it can generate heat andshrink, which can cause the crystal or the gold layer to deform orcrack. This can affect the stability, reliability, and lifetime of theopto-acoustic deflector.

To avoid these potential problems, it is important to apply a thin anduniform layer of epoxy on the steps of the deflector surface. This canbe achieved by using a precision dispenser, a flat blade or a roller tospread the epoxy evenly. The thickness of the epoxy layer should becontrolled within a certain range, depending on the type and viscosityof the epoxy, the height and pitch of the steps, and the requiredoptical and mechanical properties of the deflector. Typically, thethickness of the epoxy layer can be in the range of a few micrometers totens of micrometers, depending on the application requirements.

In one embodiment, a method for securing crystals to a gold platedoptical element includes:

-   -   placing each crystal on a moveable pedestal mounted on a piston;    -   temporarily securing each crystal to the moveable pedestal;    -   applying an epoxy to a plurality of steps on a deflector        surface;    -   placing the piston with the crystals over the plurality of        steps;    -   actuating the piston and moving each moveable pedestal to        contact the crystal with the epoxy;    -   releasing the crystal from the moveable pedestal; and    -   curing the epoxy to secure the crystal to the steps.

The method for securing crystals to a gold plated optical element usingepoxy involves the following The method for securing crystals to a goldplated optical element using epoxy involves the following steps:

Placing each crystal on a moveable pedestal mounted on a piston: Thecrystals are carefully placed on a moveable pedestal which is mounted ona piston that is capable of moving up and down.

Temporarily securing each crystal to the moveable pedestal: To preventthe crystals from falling off during the assembly process, they aretemporarily secured to the moveable pedestal using a small amount of waxor adhesive.

Applying an epoxy to a plurality of steps on a deflector surface: Asmall amount of epoxy is applied to a plurality of steps on thedeflector surface. It is important to apply the epoxy thinly and evenlyto avoid any inconsistencies in the final assembly.

Placing the piston with the crystals over the plurality of steps: Thepiston, with the crystals mounted on the moveable pedestals, iscarefully lowered over the plurality of steps on the deflector surface.

Actuating the piston and moving each moveable pedestal to contact thecrystal with the epoxy: The piston is actuated to move each moveablepedestal, and the crystals are brought into contact with the epoxy onthe steps of the deflector surface.

Curing the epoxy to secure the crystal to the steps: Once the crystalsare in place, the epoxy is cured. This is typically done by heating theassembly to a specific temperature for a specified amount of time. Thecuring process ensures that the crystals are securely attached to thedeflector surface.

It is important to note that the entire assembly process should becarried out in a clean environment, free of dust and other contaminants,to avoid any potential issues with the final product. Additionally, careshould be taken to ensure that the crystals are properly aligned withthe deflector surface to avoid any misalignment issues during use.

Due to the steps with variable heights, the piston is a gimbal that canmove in x and y axis to apply controlled pressure to the crystals and tospread the epoxy as thin as possible. The use of a gimbal allows forprecise movement of the piston in both the x and y directions, whichhelps to ensure that each crystal is pressed evenly onto the deflectorsurface even where different step heights are involved, and that theepoxy is spread evenly across the steps. This is important for achievinga strong and reliable bond between the crystals and the deflectorsurface, as well as for ensuring that the crystal positions are alignedcorrectly. The gimbal can also be used to adjust the pressure and angleof the crystals, which can be important for optimizing the performanceof the opto-acoustic deflector.

FIG. 4 shows an exemplary opto-acoustic laser system, which is a type ofsystem that combines optical and acoustic techniques for a range ofapplications, such as sensing, imaging, and spectroscopy. Some of themain components of an opto-acoustic laser system include:

-   -   Laser source 400: A laser source is used to generate the optical        radiation that interacts with the sample. Different types of        lasers can be used, depending on the specific application, such        as pulsed or continuous wave (CW) lasers.    -   Optical components: 402 Optical components are used to guide,        focus, and manipulate the laser beam. These may include mirrors,        lenses, polarizers, and filters.    -   Acoustic transducers 406: Acoustic transducers are used to        generate and detect acoustic waves that are produced by the        interaction of the laser beam with the sample. These can be        piezoelectric transducers, optical fibers, or other types of        sensors. A sample chamber is the region where the laser beam        interacts with the sample. Preferably the sample chamber is        inside an optical element such as element 10 of FIG. 1 , but in        other applications the sample chamber can be a gas cell, a        liquid cell, or a solid-state sample holder, depending on the        application.    -   Signal processing and data acquisition 420: Signal processing        and data acquisition systems are used to analyze the acoustic        signals generated by the interaction of the laser beam with the        sample. These systems may include amplifiers, filters, and data        acquisition cards.    -   Control electronics 422: Control electronics are used to        synchronize the laser and acoustic pulses, as well as to control        the various components of the system, such as the laser power,        acoustic frequency, and detection settings.

The phased array opto-acoustic system is a type of opto-acoustic imagingsystem that uses an array of optical and acoustic elements to generateand detect acoustic waves for imaging and sensing applications.

When an RF frequency acoustic wave propagates inside an opticallytransparent medium, a periodic change in the refractive index occurs dueto the compressions and rarefactions of the sound wave. This periodicvariation produces a grating capable of diffracting an incident laserbeam.

Two types of diffraction can occur:

-   -   Operation as a Raman-Nath device occurs when the laser beam        enters the sound field at normal incidence and the light-sound        interaction length L<Λ²/A, where A is    -   the laser wavelength in the medium and Λ is the sound wavelength        which is analogous to the line spacing of a thin diffraction        grating. Klein and Cook¹ have defined a parameter Q        Q=2πλL F ² /nV ²    -   where Fis the RF acoustic frequency, n the index of refraction,        and V the acoustic velocity of the interaction medium. For a Q        value of approximately 4 or less operation is said to be in the        Raman-Nath region. Operation in this mode is characterized by        the fact that many diffracted orders are generated and the        maximum amount of light in any of the diffracted orders is        limited to approximately 35 percent. This type of device is        typically used as a loss modulator for intracavity applications        that require light to be removed from the zero order or        undiffracted beam passing straight through the device; for        applications such as q-switching.    -   Operation as a Bragg device occurs when L>Λ²/λ or according to        Klein-Cook when Q is approximately 7 or greater. In this mode        the incident laser beam should enter the sound field at the        Bragg angle        θ_(B)=λ/2Λ    -   Maximum diffraction efficiency occurs when the incident laser        beam and the first order diffracted beam are adjusted to form        symmetrical angles with respect to the acoustic wavefronts.        Depending upon design, up to 90 percent of the incident light        can be diffracted into one order. Since acousto-optic devices        are not 100 percent efficient, all of the light cannot be        removed from the zero order. Since no light remains in the first        order when the sound power is removed, the first diffracted        order is used in applications such as amplitude modulation which        require a high extinction ratio.

Amplitude modulation is detailed next. Beam separation or angulardeviation between zero and first order is twice the Bragg angleθ=2θ_(B) =λFN

The separation is proportional to acoustic frequency with a highercenter frequency giving greater separation. The percentage of light 1₁in the first order or diffraction efficiency is given byθ=1₁/1=sin²(2.22[1/λ²(L/H)M ₂ P _(a)]^(1/2))

Diffraction efficiency is proportional to acoustic power (Pa),acousto-optic interaction material figure of merit (M2), sound fieldlength to height aspect ratio (UH), and inversely proportional to thesquare of the optical wavelength (1/.2).

Since the diffraction process is a sin² function please note that it ispossible to overdrive the modulator resulting in decreased diffractionefficiency. Also note that since efficiency is inversely proportional tooptical wavelength, longer wavelengths will require more RE drive power(P), and shorter wavelengths will require less RE drive power. Drivepower can be determined for optical wavelengths different from the testcondition wavelength byP ₁ /P ₂ =k(λ₁/λ₂)²

Rise time, Tr, is the time interval for the light intensity to go from10% to 90% of maximum value in response to an acoustic step function.Rise time for a Gaussian laser beam is given byTr=0.64D/V=0.64T

-   -   where Tis the transit time of the acoustic wave across a laser        beam of diameter D.

The frequency response of an acousto-optic modulator can becharacterized by the modulation index or depth of modulation (M) whichcan be calculated for a sinusoidal inputM=exp(−π² f _(m) ² T ²/8).

The 50% depth of modulation or −3 db modulation bandwidth occurs whenfmT=0.75 where fm is modulation frequency.

When viewing photodiode current (see FIG. 5 ) on an oscilloscope, theDepth of Modulation can be calculated from the maximum intensity (Imax)and minimum intensity (Imin) readings displayedM=(Imin−Imin)/(Imax+Imin)or in terms of contrast (C) whereC≡I _(max) /I _(min)M=(C−1)/(C+1).

Optical frequency shifting can be done. Because the acoustic wavetravels across the optical beam, the optical frequency undergoes aDoppler shift by an amount equal to the acoustic frequency. TheModulator can up-shift or down-shift the optical frequency depending onthe orientation of the optical beam in relation to the sound field. Ifthe laser beam enters the sound field at the Bragg angle in oppositionto the direction of the sound field, the optical frequency is up-shifted(plus first order) and if the beam enters at the Bragg angle in the samedirection as the sound field, the optical frequency is down-shifted(minus first order).

Deflection is detailed next. Since the angular position of the firstorder beam is proportional to acoustic frequency, an incrementalfrequency change will produce an incremental angular deviationΔθ=λΔFN

Total deviation is limited by the transducer electrical bandwidth.

Deflector resolution N, the number of resolvable beam positions acrossthe total scan angle is defined as the total scan angle divided by thediffraction spread of the laser beam. For a uniformly illuminatedoptical beamN=(λΔFN)/(λ/D)=(D/V)ΔF=TΔF

Since r is the transit time of the acoustic wave across the beamdiameter D and IIF is the RF bandwidth of the device, the product of thetwo is called Time Bandwidth product. Since r is the time for sound tofill or clear the optical aperture, it limits the spot position accesstime in a random access application.

The far field light intensity pattern for the deflected beam is a (sinx/x)2 function. By the Rayleigh Criterion the above resolution occurswhen the maximum intensity at one beam position coincides with theintensity minimum at an adjacent beam position.

Changing frequency from the nominal center RF frequency to deflect thelaser bears destroys the Bragg angle symmetry condition for efficientdiffraction efficiency, resulting in reduced diffraction efficiency atthe edges of the scan bandwidth. Incorporating acoustic phased arraybears steering in the deflector design will maintain a high diffractionefficiency across the total deflection bandwidth since the acousticwavefronts effectively rotate in response to a change in frequency tomaintain the proper Bragg condition. Acoustic phased array beam steeringis accomplished by mechanically cutting into the glass a series of smallsteps which are one half of an acoustic wavelength high at centerfrequency and phasing adjacent piezoelectric transducers 180 degreesapart. This technique causes the acoustic wavefronts to effectivelyrotate in response to a change in applied RF frequency. Because of thebeam steering high uniform diffraction efficiency occurs only on oneside of the zeroth order beam as the RF frequency is swept from minimumto maximum. On the opposite side of zero order the Bragg condition issatisfied for only one frequency. As the RF frequency is repetitivelyswept across the entire range, the position for high diffractionefficiency will change in response to mechanically rotating thedeflector.

In linear scanning applications where T, total scan time, is short, afrequency gradient is produced across the optical aperture. Thefrequency gradient acts like a cylinder lens of fixed focal length fl=VT/68, either converging or diverging the diffracted beam. If total scantime T is short, the cylinder effect will preclude bi-directionalscanning. The effect can be compensated for in a unidirectional fixedscan rate system by adjusting the beam shaping optics used to expand Dfor resolution purposes.

Multiple beam generation is detailed next. Every acoustic frequency inan acousto-optic device defines a unique angular beam position. Ifseveral acoustic frequencies are applied simultaneously to theacousto-optic device, a corresponding number of diffracted beams will becreated.

Separation Between Beams isΔθ=λΔFN

-   -   where ΔF is the acoustic frequency difference between diffracted        beams. Each beam can be modulated independently but the        intensities of the beams are interrelated.

One AOD deflector embodiment operates at 40 MHz and 60 MHz with highefficiency and equal intensity. Optical grade, single crystal Germaniumis used for the interaction medium and Lithium Niobate piezoelectrictransducers are used to generate the RF frequency acoustic travelingwave inside the Germanium.

The RF center frequency of operation is 50 MHz and the height of thesound field or active aperture is 10 mm. RF frequencies of operation are40 MHz and 60 MHz. The Germanium optical surfaces are coated with amulti-layer dielectric antireflection coating designed for operation at9.4 μm. In this embodiment, the pulse rise time, Tr (10% to 90%), anddepth of modulation are determined by the light beam diameter D. ForModel AGD-5147 with acoustic velocity V=5.5 mm/μsecTr=117D nsec

-   -   where D is in mm. Modulation response for sinusoidal inputs can        be calculated as        M=exp(−4.08×10⁻² D ² f _(m) ²)    -   where D is beam diameter in mm and fm is modulation frequency in        MHz. For a deflector, a large beam width is required to obtain        full resolution. This precludes operation as a high speed        modulator.

The frequency shift range is plus or minus 40 MHz to 60 MHz depending onwhether the plus or minus diffracted order is used. The Deflectorproduces two first order, diffracted, optical beams with an angularseparation of 34.2 mad. At 9.4 um, a frequency deviation of 20 MHzcentered at 50 MHz will produce an angular separation of 34.2milliradians centered 85.4 milliradians from the undeflected light. Thetwo optical beams can be individually amplitude modulated.

The optical beam is aligned parallel to the sound field and adjust thevertical position to assure that the total optical beam is in the soundfield. Initially, set the device 10 optical face nearly normal to thelight beam, apply 50 watts RF power at 60 MHz and rotate the device toadjust the Bragg angle so that optimum first order light intensity isobtained. Change RF frequency to 40 MHz with 50 watts RF power and notethe diffraction efficiency. The 40 MHz and 60 MHz efficiencies should beclose. Slightly adjust the Bragg angle condition so that equalintensities are obtained at both RF frequencies. After equal intensitiesare obtained, adjust RF drive power to 120 Watts. Once again check bothefficiencies. A slight adjustment may be needed to obtain equalintensities. The zero and unwanted diffraction orders can be spatiallyfiltered with an aperture.

The device of FIG. 1 can be used in a number of applications. Forexample, the device can be used in laser modulators and deflectors whichare devices used in laser systems to modify the behavior of laser beams.The laser modulator is a device that changes the properties of a laserbeam as it propagates through a medium. It can be used to control theintensity, phase, or polarization of the beam. The modulators can bemade using materials that have nonlinear optical properties, such aslithium niobate, which allows for the manipulation of the laser beam.The laser deflector is a device that changes the direction of a laserbeam. It can be used to steer the beam to a particular location or toscan the beam over a surface.

FIG. 5 shows an exemplary laser microscopy system with phased-array AOD.Acousto-optic systems are increasingly being used in advanced microscopyfor a wide range of applications, including optical imaging,super-resolution microscopy, and fluorescence lifetime imaging. Theintegration of acousto-optic devices into advanced microscopy systemsprovides several advantages, such as fast switching speeds, precisecontrol over light intensity and polarization, and the ability torapidly scan multiple focal planes. As shown in FIG. 5 , the componentsof a Laser Scanning Microscope (LSM) with Phased Array Acousto-OpticDeflector (AOD) include:

-   -   Laser: A laser source provides a highly focused and intense beam        of light, usually at a single wavelength, which is used to        excite the sample.    -   Optics: A series of lenses, mirrors, and other optical        components are used to shape, focus, and scan the laser beam        across the sample.    -   Acousto-optic deflector: A phased array AOD is used to rapidly        scan the laser beam across the sample in two dimensions. The AOD        consists of a crystal that is driven with a high-frequency        acoustic signal, which creates a moving grating that deflects        the laser beam.    -   Sample stage: A precision motorized stage is used to move the        sample in three dimensions, allowing the laser to be focused at        different depths within the sample.    -   Detector: A detector collects the emitted light from the sample,        which is then processed and displayed as an image.    -   Control electronics: The control electronics include a computer,        which is used to control the laser, AOD, and sample stage, as        well as to process and display the resulting images.

The LSM with phased array AOD provides a high-speed, high-resolutionimaging technique that can be used for a variety of applications inbiology, materials science, and other fields. The LSM uses a focusedlaser beam to scan a sample, providing high-resolution images of itssurface. LSM is used in a variety of applications, including biologicaland material sciences. The phased array AOD is used in LSM systems tocontrol the laser beam's position and intensity as it scans across thesample. The AOD is typically placed in the laser path before theobjective lens, which focuses the beam onto the sample. The AOD works byusing sound waves to create an acoustic gradient that diffracts thelaser beam. By applying different frequencies to different parts of theAOD, the beam can be steered in different directions or focused todifferent points in the sample. This allows for precise control over theposition and intensity of the laser beam as it scans the sample. Adetector measures the intensity of the laser beam as it scans thesample. The detector sends this information to a computer, whichconstructs an image of the sample based on the laser's intensity at eachpoint.

The LSM with phased array AOD offers several advantages over other typesof microscopy. For example, it allows for high-resolution imaging ofliving samples, as the laser beam can be focused on a single pointwithout damaging surrounding tissue. It also enables 3D imaging byscanning the laser beam through the sample at different depths.

In one embodiment, the laser scanning microscopy system includes

-   -   a laser for providing a light source;    -   a scanning system for scanning the laser beam across a sample;    -   a detector for detecting emitted light from the sample;    -   a phased array acousto-optic deflector (AOD) for controlling the        direction and intensity of the laser beam.

A computer processor can be programmed to control the AOD and scanningsystem to generate 2D or 3D images of the sample. The AOD can bemultiple AODs operating at different frequencies to achieve high-speedand accurate beam steering. The AOD is used for performing optogeneticsby delivering light to specific regions of a sample. The AOD is used forperforming fluorescence lifetime imaging microscopy (FLIM) bycontrolling the laser beam intensity and timing. The AOD is used forperforming stimulated emission depletion (STED) microscopy by modulatingthe laser beam intensity to create super-resolution images. The AOD isused for performing two-photon excitation microscopy (2PEM) bycontrolling the laser beam intensity and frequency to excitefluorophores deep within a sample. An adaptive optics system can be usedfor correcting for aberrations in the laser beam path. A confocal systemcan be used for reducing out-of-focus light and improving imagecontrast.

The system operates as follows. The method includes

-   -   providing a light source with a laser;    -   controlling the direction and intensity of the laser beam using        a phased array AOD;    -   scanning the laser beam across a sample;    -   detecting emitted light from the sample to generate an image of        the sample.

The method of claim 10, further comprising using the AOD for performingoptogenetics by delivering light to specific regions of a sample.

The AOD can be used for performing FLIM by controlling the laser beamintensity and timing. The AOD can perform STED microscopy by modulatingthe laser beam intensity to create super-resolution images. The AOD canalso perform 2PEM by controlling the laser beam intensity and frequencyto excite fluorophores deep within a sample. The system can correct foraberrations in the laser beam path using an adaptive optics system.

The AOD and FLIM (Fluorescence Lifetime Imaging Microscopy) t can beused together to create highly precise and detailed imaging ofbiological tissues and structures. AODs are devices that use acousticwaves to deflect a laser beam, allowing for the rapid and precisescanning of the beam over a sample. In LSM, this scanning process isused to create high-resolution 3D images of biological structures. FLIM,on the other hand, is a technique used to measure the fluorescencelifetime of a sample. By measuring the time it takes for a fluorescentmolecule to decay from its excited state to its ground state, FLIM canprovide information about the chemical and physical environment of themolecule. By combining AOD and FLIM technologies, researchers can createhighly detailed images of biological samples with information about thechemical and physical environment of the sample. This allows for abetter understanding of biological processes and can aid in thedevelopment of new drugs and treatments.

The AOD can also be used in stimulated emission depletion (STED)microscopy, a type of superresolution microscopy that provides higherspatial resolution compared to conventional confocal microscopy. In STEDmicroscopy, a laser beam is focused on a sample and stimulatesfluorescent molecules to emit light. However, this method still suffersfrom the diffraction limit of light, which limits the resolution. Toovercome this limitation, a second beam with a doughnut-shaped intensityprofile is overlaid on the laser beam, causing fluorescence to bequenched in the periphery of the focal spot, leaving only a small areain the center to emit light. This results in a much higher resolutionimage, as the size of the focused spot can be smaller than thediffraction limit. AODs are used in STED microscopy to shape thedoughnut-shaped depletion beam, which is scanned across the sample tocreate the high-resolution image. The AOD is used to deflect thedepletion beam in different directions, allowing for rapid and precisescanning of the beam. The high-speed scanning is necessary to create thefinal image, as the depletion beam must be scanned across the samplemultiple times to create a complete image. The use of AODs in STEDmicroscopy allows for precise control of the depletion beam and rapidscanning of the sample, resulting in high-resolution images that are notpossible with conventional confocal microscopy.

The AOD can also be used in conjunction with two-photon excitationmicroscopy (2PEM), a powerful imaging technique that allows forhigh-resolution, three-dimensional imaging of biological tissues. In2PEM, a laser beam is used to excite fluorescent molecules within thesample, and the resulting fluorescence is detected to generate an image.Because the excitation is localized to a very small volume of thesample, 2PEM enables imaging at much greater depths than traditionalmicroscopy techniques. AODs can be used in 2PEM to rapidly scan thelaser beam across the sample, allowing for high-speed imaging of largeareas. This is important for time-lapse imaging and for capturingdynamic events in living tissues. AODs can also be used to selectivelytarget specific regions of the sample for excitation, allowing forprecise control over the imaging process. In addition to their use inscanning and targeting the laser beam, AODs can also be used incombination with other optical elements to shape the beam profile or tomodulate its intensity. This allows for even greater control over theexcitation process and can be useful in applications such asoptogenetics, where light is used to control the activity of specificcells within a tissue.

One application of acousto-optic systems in advanced microscopy is forfast optical sectioning. By using a combination of acousto-opticdeflectors and tunable lenses, researchers can rapidly switch betweendifferent focal planes, allowing them to capture 3D images with hightemporal resolution. This approach is particularly useful for studyingdynamic biological processes, such as cell division or proteininteractions, where changes can occur rapidly and at multiple depths.

Another application of acousto-optic systems is for super-resolutionmicroscopy. By using acousto-optic deflectors to scan the laser beam ina controlled pattern, researchers can generate a high-resolution imageof the sample. This approach is particularly useful for studying smallstructures, such as individual molecules or subcellular structures,where traditional imaging techniques may not provide sufficientresolution.

Acousto-optic systems are also useful for fluorescence lifetime imaging,which is a technique used to study the dynamics of fluorescent moleculesin cells and tissues. By using acousto-optic modulators to control theexcitation laser intensity and timing, researchers can measure thefluorescence lifetime of different molecules in the sample. Thisprovides valuable information about the interactions between moleculesand the local environment, which can be used to study a wide range ofbiological processes.

Acousto-optic systems provide a powerful tool for advanced microscopy,enabling researchers to study complex biological systems with highspatial and temporal resolution. As the technology continues to develop,it is likely that acousto-optic systems will become increasinglyintegrated into a wide range of microscopy platforms, enabling newinsights into the fundamental processes of life.

The invention has been described with reference to the preferredembodiments. Obviously, modifications and alterations will occur toothers upon reading and understanding the preceding detaileddescription. It is intended that the invention be construed as includingall such modifications and alterations insofar as they come within thescope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A laser scanning microscopy system comprising: alaser for providing a light source; a scanning system for scanning thelaser beam across a sample; a detector for detecting emitted light fromthe sample; and a phased array acousto-optic deflector (AOD) including aplurality of transducers electrically coupled in parallel with first andsecond radio frequency (RF) inputs for controlling the direction andintensity of the laser beam into two different paths depending on thefirst and second RF inputs.
 2. The system of claim 1, wherein the AODcomprises multiple AODs operating at different frequencies in one deviceto achieve high-speed and accurate beam steering.
 3. The system of claim1, wherein the AOD delivers light to specific regions of a sample forperforming optogenetics.
 4. The system of claim 1, wherein the AODcontrols the laser beam intensity and timing and performs fluorescencelifetime imaging microscopy (FLIM).
 5. The system of claim 1, whereinthe AOD is used for performing stimulated emission depletion (STED)microscopy by modulating the laser beam intensity to createsuper-resolution images.
 6. The system of claim 1, wherein the AOD isused for performing two-photon excitation microscopy (2PEM) bycontrolling the laser beam intensity and frequency to excitefluorophores deep within a sample.
 7. The system of claim 1, furthercomprising an adaptive optics system for correcting for aberrations inthe laser beam path or a confocal system for reducing out-of-focus lightand improving image contrast.
 8. The system of claim 1, comprising: anoptical element having a surface with one or more steps formed thereon;a conductive layer formed on the surface with the steps; one or morecrystals secured to each step; and electrodes positioned on each surfaceof each crystal.
 9. The system of claim 1, comprising a tuning elementto match a predetermined impedance.
 10. The system of claim 1,comprising a tuning element providing an output impedance of 50 ohms.11. The system of claim 1, comprising a tuning element includinginductive and capacitive passive components.
 12. The system of claim 1,comprising tuning element comprises 1:1 balun, 4:1 transformer, acapacitor, and an inductor.
 13. The system of claim 1, wherein the AODcomprises an optical element with a slanted end.
 14. The system of claim13, wherein the slanted end comprises a compound angle to move reflectedsound field out of a laser beam working range.
 15. The system of claim13, wherein the slanted end forms a 30 degree angle measured from a longside of the optical element to a short side of the optical element. 16.The system of claim 13, wherein a surface of the slanted end comprises a2 degree slope.
 17. The system of claim 13, wherein the optical elementcomprises germanium, tellurium dioxide (TeO2), lithium niobate, PZT,fused silica, chalcogenide glasses, glass.
 18. The system of claim 1,wherein a tuning element matches a deflector output impedance at 40 MHzand at 60 MHz to a 50 ohm impedance.
 19. The system of claim 13, whereinthe optical element comprises a slanted end, wherein the slanted endcomprises a compound angle to move reflected sound field out of a laserbeam working range, wherein the slanted end forms a 30 degree anglemeasured from a long side of the optical element to a short side of theoptical element, and wherein a surface of the slanted end comprises a 2degree slope, and wherein the optical element comprises germanium,tellurium dioxide (TeO2), lithium niobate, PZT, fused silica,chalcogenide glasses, glass.
 20. A method to perform microscopy,comprising: providing a light source with a laser; controlling thedirection and intensity of the laser beam using a phased array AOD withone or more steps and a plurality of transducers electrically coupled inparallel and bonded to a crystal using an epoxy with first and secondinputs that determine two different laser beam paths; scanning the laserbeam across a sample; detecting emitted light from the sample togenerate an image of the sample; applying the laser beam to an opticalelement having one or more steps each with a predetermined height andone or more crystals or transducers on the one or more steps; impedancematching the electrical input of the transducers to a predeterminedimpedance load; providing an electrical input to deflect the laser atthe two or more frequencies; and generating a sound field in the opticalelement to deflect a laser beam based on two or more frequencies.